Signal acquisition probes used with signal measurement instruments, such as oscilloscopes, logic analyzers and the like have a probe body with single ended or differential probing tips extending from one end of the probe body and a signal cable extending from the other end of the probe body. The single ended or differential proving tips are coupled to passive circuitry or passive/active circuitry within the probe body. The circuitry within the probe body conditions the signal under test for coupling to the signal measurement instrument via the signal cable. Signal acquisition probes of this design have a maximum bandwidth in the range of 6 GHz.
The frequency output and response of electronic circuits continues to increase. Further, the separation between circuit components, circuit traces, electrical contact pads and the like in circuit board layouts continue to decrease. These developments require the use of signal acquisition probes having reduced size and increased bandwidth for coupling signals under test to signal measurement instruments. Signal acquisition probes with probe tips extending from the probe body are bulky and cumbersome to use on these types of circuit boards.
The highest bandwidth of signal acquisition probes used with real time digital oscilloscopes range from 13 to 16 GHz. The design of these high frequency signal acquisition probes differs from the design of previous signal acquisition probes. Because of the gigahertz frequencies these probes acquire, the signal under test need to be launched into a coaxial signal path to prevent degradation and loss of fidelity of the test signal. These high frequency signal acquisition probes have a probe body with one or more coaxial cables extending from one end. The free end(s) of the coaxial cable(s) are coupled to probing tip(s) having associated electrical circuitry. The signal(s) under test are acquired at the probing tip(s) and coupled through the electrical circuitry of the probing tip(s) into the coaxial cable(s). The coaxial cable(s) couple the acquired signal(s) under test to active circuitry in the probing head. The active circuitry condition(s) the acquired signal(s) and couples the resulting signal(s) to the oscilloscope.
U.S. Pat. Nos. 7,056,134 and 7,017,435 teach a probing tip system for a signal acquisition probe and a hand held probing adapter for the signal acquisition probe. The coaxial cables exit directly from the probe body with the coaxial cables coupled to a probing tip member. The probing tip member includes circuitry coupled to the coaxial cables and to the probing tips. Various types of probing tip(s) may be positioned on the probing tip member to allow soldering of the probing tip(s) to electrical contacts on the device under test. Variable spacing probing tips may be placed on the probing tip member with the probe body and the probing tip member being secured into a probing adapter for hand-held probing. The probing adapter has elastomeric compliant members disposed against the probing tip member to allow for axial and lateral rotation displacement of the probing tip member.
U.S. Published Patent Application No. 2007/0063714 shows coaxial connectors mounted on the probe body with the coaxial connectors coupled to the active circuitry in the probe body. The coaxial connectors mate with corresponding coaxial connectors disposed on the ends of semi-rigid coaxial cables. The other ends of each of the coaxial cables are coupled to an impedance element, such as a resistor, which is coupled to a probing tip. Each semi-rigid coaxial cable has a spring portion disposed between the probe tip and the coaxial connector. Pressure placed on the probe tips results in some give within the spring portion permitting some compliance to maintain contact with test points on the device under test in the presence of normal hand movement. Each semi-rigid coaxial cable has a slider on it that moves along the semi-rigid coaxial cable and a retention loop disposed close to the probing tip. A ground wire passes through the retention loops and is secured to the sliders on each of the semi-rigid coaxial cables. Moving the sliders along the semi-rigid coaxial cables decreases or increases the spacing between the retention loops which in turn decreases or increases the spacing between the probing tips.
U.S. Pat. No. 7,102,370 describes a compact micro-browser for hand held probing. The micro-browser has a pair of sleeves disposed in a grip shaped to be rotated between the thumb and finger. A pair of rods are retained in bores in the sleeves with a circuit board soldered to the distal ends of each rod. Each circuit board has a coupling network with on end connected to a probing tip and the other end coupled to a length of coaxial cable that passes through an axial slot in grip. The other end of the coaxial cables have coaxial connectors that mate with corresponding coaxial connectors in a probe body, such as described in of U.S. Published Patent Application No. 2007/0063714. One of the rods is allowed to rotate within its bore in the sleeve, while the other is held stationary by a notch in the sleeve. The rotatable rod has a captive spring that resists the force of the probe contact. The distance between the probing tips is a function of the amount of rotation of the grip.
U.S. Pat. No. 7,212,018 describes a dual probe tip having a tip portion of a probe and a rigid portion where a locking mechanism selectively fixes and allows movement of the tip portion relative to the rigid portion. The tip portion has a pair of probe support arms joined together at one end of the probing arms. Disposed at the other end of the probing arms are probing tips that are connected to a flex circuit having a flex bridge for placing the flex circuitry along both arms. The flex circuitry extends along the inner surface of one of the probe arms with the end of the flex circuitry terminating an external coupler. An arm positioning mechanism is disposed between the probing arms for changing the relative positions of the probing tip to each other. The locking mechanism is fixed to one end of the rigid member and includes a ball joint having an extension on which the probe support arms are secured. A number of embodiments are described for locking and releasing the ball joint. Releasing pressure on the ball joint allows the movement of the probing tips mounted on the probe support arms relative to the rigid portion. Applying pressure on the ball joint locks the probe support arms relative to the rigid portion.
Each of the above described devices has some form of probing tip compliance. Some have axial and lateral rotation compliance. Others rely on the flexibility of the probing tips to provide compliance while still others rely or on the flexibility of the probing tips and the structure supporting the probing tips to provide the compliance. While all of the devices provide some form of probing tip compliance, generally they provide the highest level of compliance with the probing tips vertical to probing points on a device under test. If the devices are angles to the probing points, more of the needed compliance is taken up by the probing tips themselves. Generally, it takes less downward force to bend or break probing tips when the probing tips are at an angle to the probing points than when the probing tips are vertical to the probing points. It is preferable to have a probing tip system where a single element provides substantially all of the compliance required to the probing tips.